This invention relates to a method of controlling a hydraulic brake system for a vehicle provided with a hydraulic pressure source for generating brake hydraulic pressure.
In recent years, in order to achieve sophisticated behavior control of a vehicle and a light brake feeling, as disclosed e.g. in Japanese patent publication 2590825, a brake system is employed which is provided with a hydraulic pressure source for generating brake hydraulic pressure and actuates a driving device for the hydraulic pressure source based on a detection signal from a brake operating force detecting means for detecting the operating force applied to a brake operating member.
Among brake systems of such a hydraulic pressure source-driven type, there is one having a fail-safe function which has a master cylinder for producing hydraulic pressure corresponding to the operating force applied to the brake operating member, the master cylinder communicating with wheel cylinders through master cylinder passages having on-off valves, and opens the on-off valves to transmit the hydraulic pressure of the master cylinder as brake hydraulic pressure if the hydraulic pressure source does not operate normally.
In a brake system of such a conventional hydraulic pressure source-driven type, since there is a delay in response between the detection of the operating force by the brake operating force detecting means and the activation of the hydraulic pressure source for producing brake hydraulic pressure, compared with a conventional master cylinder-direct-connect type, rise in the brake hydraulic pressure is slow, so that the driver feels some delay in the brake effect.
Also, a brake control member such as a brake pedal usually has an initial play area in its operating amount. Thus, in a hydraulic pressure source-driven type brake system as described above, a time from the start of brake operation to actuation is equal to the sum of the time needed to depress the pedal for the initial play area and the abovementioned delay in response. Thus it is possible that the effect of the brake does not appear in time especially during urgent braking.
An object of this invention is to provide a method of controlling a hydraulic pressure source-driven type vehicle hydraulic brake system with which the driver does not feel a delay in the effect of braking, and in which the braking force operates quickly and reliably even during urgent braking.
According to this invention, there is provided a method of controlling a vehicle hydraulic brake system the brake system has a brake operating member having an initial play area, a brake operating force detecting means for detecting an operating force of the brake operating member produced when the brake operating amount of the brake operating member exceeds the initial play area, a hydraulic pressure source for producing brake hydraulic pressure in a wheel cylinder, a driving device for the hydraulic pressure source, a fluid passage for communicating the hydraulic pressure source with the wheel cylinder, and a relief passage communicating with the wheel cylinder through an on-off valve, and the driving device for the hydraulic pressure source being actuated based on a detection signal from the brake operating force detecting means, characterized in that a brake operating amount detecting means for detecting the brake operating amount in the initial play area is provided, a threshold is set at a predetermined position in the initial play area, and that the driving device for the hydraulic pressure source is actuated beforehand when the brake operating amount detecting means detects that the brake operating amount has reached the threshold.
That is, the brake operating amount detecting means for detecting the brake depressed amount in the initial play area of the brake operating member is provided, and by activating the device for driving the hydraulic pressure source beforehand when the brake operating amount detecting means detects that the brake operating amount has reached a predetermined threshold, the time needed for the brake depressed amount in the initial play area and the response delay of the device for driving the hydraulic pressure source are overlapped to shorten the time from the start of brake operation to the actuation of the brake.
This method of controlling a vehicle hydraulic brake system can be used to a brake system which further comprises a master cylinder for producing hydraulic pressure corresponding to the operating force of the brake operating member, and a master cylinder passage through which the master cylinder and the wheel cylinder communicate with each other through an on-off valve, and wherein the hydraulic pressure produced in the master cylinder is transmitted to the wheel cylinder by selectively opening and closing the on-off valve in the master cylinder passage.
In the method of controlling a vehicle hydraulic brake system, the on-off valve in said relief passage is opened beforehand, and is closed when the brake operating amount detecting means or the brake operating force detecting means detects that the brake operating amount has reached the terminal position of the initial play area. Thus it is possible to shorten the time from the start of brake operation to the actuation of the brake while ensuring the play function of the brake operating member.
In the brake system having the master cylinder passage, when the device for driving the hydraulic pressure source is activated beforehand, the on-off valve in the master cylinder passage may be opened beforehand, and closed when the brake operating amount detecting means or the brake operating force detecting means detects that the brake operating amount has reached the terminal position of the initial play area.
By detecting the operating speed of the brake operating member in the initial play area by the brake operating amount detecting means, and increasing the driving force of the driving device for the hydraulic pressure source which is activated beforehand according to the operating speed, it is possible to increase the rising speed of the brake hydraulic pressure depending upon the degree of urgency of the brake, which corresponds to the operating speed of the brake operating member and thus to make the magnitude of the braking force and the brake working speed more suitable. When the operating speed of the brake operating member is slow because no urgency is needed, the driving force by the driving device can be decreased to minimize energy loss.
Other features and objects of the present invention will become apparent from the following description made with reference to the accompanying drawings, in which: